Recent work in the field of olefin upgrading has resulted in a catalytic process for converting lower olefins to heavier hydrocarbons. Heavy distillate and lubricant range hydrocarbons can be synthesized over ZSM-5 type catalysts at elevated temperature and pressure to provide a product having substantially linear molecular conformations due to the ellipsoidal shape selectivity of certain medium pore catalysts.
Conversion of olefins to gasoline and/or distillate products is disclosed in U.S. Pat. Nos. 3,960,978 and 4,021,502 (Givens, Plank and Rosinski) wherein gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins are converted into an olefinic gasoline blending stock by contacting the olefins with a catalyst bed made up of a ZSM-5 type zeolite. Particular interest is shown in a technique developed by Garwood, et al., as disclosed in European patent application No. 83301391.5, published Sept. 29, 1983. In U.S. Pat. Nos. 4,150,062; 4,211,640 and 4,227,992 Garwood et al disclose the operating conditions for the Mobil Olefin to Gasoline/Distillate (MOGD) process for selective conversion of C.sub.3 + olefins to mainly aliphatic hydrocarbons.
In the process for catalytic conversion of olefins to heavier hydrocarbons by catalytic oligomerization using a medium pore shape selective acid crystalline zeolite, such as ZSM-5 type catalyst, process conditions can be varied to favor the formation of hydrocarbons of varying molecular weight. At moderate temperature and relatively high pressure, the conversion conditions favor C.sub.10 + aliphatic product. Lower olefinic feedstocks containing C.sub.2 -C.sub.8 alkenes may be converted; however, the distillate mode conditions do not convert a major fraction of ethylene. A typical reactive feedstock consists essentially of C.sub.3 -C.sub.6 mono-olefins, with varying amounts of nonreactive paraffins and the like being acceptable components.
In the past various methods have been employed for preparing surface-inactive catalysts. Several techniques may be used to increase the relative ratio of intra-crystalline acid sites to surface active sites. This ratio increases with crystal size due to geometric relationship between volume and superficial surface area. Deposition of carbonaceous materials by coke formation can also shift the effective ratio. Enhanced effectiveness is observed where the surface acid sites of small crystal zeolites are reacted with a chemisorbed organic base or the like.
Catalysts of low surface activity can be obtained by using medium pore zeolites of small crystal size that have been selectively deactivated by basic compounds, such as bulky amines and/or phosphines having an effective critical dimension or cross section diameter of about 6-7 Angstrom or greater. Another surface modification technique is deactivation by treating with metal compounds.
The catalysts may be treated with organic silicon compounds, as described in U.S. Pat. Nos. 4,100,215 (Chen) and 4,002,697 (Chen) to impart the desired degree of surface deactivation while being essentially free of carbonaceous deposits. Such treatment involves contacting the catalyst with a silane surface modifying agent capable of deactivating catalytic (acidic) sites located on the external surface of the zeolite by chemisorption.
It is a main object of this invention to provide an improved process for upgrading olefins to valuable lubricant 1 quality product. Significantly improved linearity can be achieved by employing a catalyst comprising a medium pore shape selective siliceous metallosilicate with a substantially inactive surface.